1. Field of the Invention
The present invention relates to an electrophotographic photoconductor with high durability and high image quality. The present invention also relates to an electrophotographic process, an electrophotographic apparatus and a process cartridge for the electrophotographic apparatus which utilize the electrophotographic photoconductor respectively.
2. Description of the Related Art
In recent years, information processing systems have achieved remarkable advance along with the progress of the related apparatuses employing electrophotography. In particular, laser printers and digital copiers have significantly enhanced the printing quality and reliability in which the image recordings of them are conducted based on lights through transferring information into digital signals. In addition, the information processing systems have been applied progressively to laser printers and digital copiers capable of full-color printing in combination with the advanced high-speed technology. Therefore, the compatibility of high image quality and high durability has been demanded for photoconductor performance in particular.
The photoconductors utilized for the electrophotographic laser printers and digital copiers are generally base on organic photosensitive material from the viewpoint of lower cost, higher productivity, and less environmental pollution. Examples of the organic electrophotographic photoconductor include the type of photoconductive resin such as polyvinyl carbazol (PVK), the type of charge-transferring complex such as PVK-TNF (2,4,7-trinitrofluorenone), the type of pigment dispersion such as phthalocyanine binder, and the type of discrete function that combines charge-generating material with charge-transporting substance.
The mechanism of latent electrostatic-image formation in the discrete function type of photoconductor is as follows: the photoconductor is charged and irradiated with light, the light passes through a charge-transporting layer, and is absorbed by a charge-generating substance in the charge-generating layer to generate a charge; the charge thus generated is implanted into the charge-transporting layer at the interface of the charge-generating layer and charge-transporting layer, moves through the charge-transporting layer due to the electric field, and forms the latent electrostatic image by neutralizing the surface charge on the photoconductor.
However, when such organic photoconductors are utilized repeatedly, film scrapings tend to occur; when the film scrapings of the photoconducting layer come to significant, the charging potential of the photoconductor is likely to decrease, the photosensitivity tends to be deteriorated, the background smear comes to apparent due to such flaws on the photoconductor surface, and lower image density and inferior image quality tend to be seriously promoted; as such, the lower wear resistance of the photoconductor has been a serious problem in the art. Furthermore, higher durability of the photoconductor has been demanded more importantly, along with higher speed of electrophotographic apparatuses or smaller size of photoconductors, in recent years.
On the other hand, smaller and spherical toners are recently interested in the market associated with the requirement of higher image quality. However, the smaller and spherical toners have cause such a problem as lower cleaning ability due to the inherently higher mobility, inducing image degradation in terms of the toner filming or fusion, which is a serious problem to be solved.
In order to solve such problems, Japanese Patent Application Laid-Open (JP-A) No. 05-45920 and No. 2000-19918 disclose the addition of fine particles of fluorine-contained resin into the surface layer of photoconductor as a lubricant so as to promote separation at the surface. These proposals are effective by virtue of the decreased friction coefficient initially; however, the cleaning system and the toner should be controlled severely, and the reliability of surface separation is not sufficient under the repeated usage against the degradation or fluctuation of the related parts associated with the prolonged life of the photoconductor.
Further, JP-A No. 8-160648 discloses that the inclusion of polytetrafluoroethylene powder into the surface layer of photoconductor and incorporation of specific charge-transporting substances having a specific structural formula may lead to a photoconductor having high durability against surface abrasion due to wear and tear and may provide an electrophotographic photoconductor having high durability without image blurs, along with superior cleaning ability and without the toner adhesion on the photoconductor surface layer. However, since a large amount of fine particles of the fluorine-contained resin is employed, the compounds exemplified in the application cannot be expected to obtain sufficient effects. Furthermore, the redox potentials are likely to be lower and variable spontaneously, to form electric traps, and to cause the increase of residual potential.